The need for evidence of tampering with packaged products has been a perennial problem and with merchandizing activities more and more centered in large, unsupervised markets the need is greater than ever.
In general, commercially available tamper evident closures for capped container and bottle have not been satisfactory. They are costly, require additional packaging operations, compromise recycling, may be harmful and give ambiguous results. One or more of these drawbacks are present in currently available seals, bands and multicomponent or multifunctional caps.
One current method for producing such evidence in bottled products calls for the use of wafer-like seals under the cap, sealed to the bottle opening and barring access to the bottle contents until removed. Various methods of application and materials are used for a variety of products. Another method uses a plastic or metal band intimately covering the cap and adjacent neck to prevent access to the cap without removal of the band. Such methods are popularly used on bottles for wine and medicinal products. These wafer-like seals and external bands perform the task of producing evidence of tampering but only if the purchaser or user is familiar with the makeup and appearance of the unopened package because these items are separable from the primary package of cap and bottle and no explicit evidence remains. An additional handicap of such devices is the extra cost in materials, packaging machinery and the cost of operating such machinery.
Another method of providing tamper-evidence for bottles is to use caps with extended skirt portions which engage restraining features in the bottle neck and which must be gripped and torn away before the cap can be removed. This method suffers from the handicap that explicit evidence of tampering does not remain with the primary package. In other words, the torn-away lower cap portion is completely separated from the cap and container and is no longer present as a tamper indicator.
Other methods for producing tamper evidence in containers are accomplished using a perforated breakaway lower skirt portion of a metal or plastic cap on a threaded bottle neck engaged by the neck and broken away by normal cap removal procedure and retained on the bottle neck. This leaves the evidence of tampering on the package where, upon examination, it can be seen as a separated portion of the cap. However, metal caps leave a metal ring on the bottle neck which can have sharp edges and which also present a recycling problem for the bottle. Efforts to solve this problem have resulted in a metal cap with a lower skirt portion which splits radially to leave the cap in one piece when the bottle is opened. Unfortunately, solving the one problem has led to another which is the difficulty in determining whether the bottle has been opened since a careful examination is required, in most instances, to determine whether the skirt has split. Additionally, the effectiveness of the breakaway or split skirt in metal caps is a function of the control over the operation of forming the threads and breakaway feature. These are configured "in situ" on the bottle neck by a "roll-on" mechanism. Some incidence of faulty tamper evidence features are commonly known to occur during this operation which may lead to the erroneous conclusion that bottles have been tampered with.
Similarly, plastic caps with tamper indicating breakaway lower skirt portions also can falsely indicate tampering. For example, when the skirt portions are heat-shrunk in place in the capping operation ruptures can occur because of overheating. Further, the lower skirt portions commonly are connected to the cap proper with posts of small cross section spaced around the periphery of the cap which are stretched and broken during cap removal. These posts must be fragile enough to break during normal twist off procedures without requiring excessive removal torques. This presents a problem in withstanding stresses encountered during application of the cap to the bottle or by carrying in or removing from multipackage carriers which grip the bottle below the cap, and notwithstanding the fragile nature of the posts, they often cause undesirable levels of removal stress and torque. During cap removal each interconnecting post goes through a typical tensile stress failure with a consistent build up of stress level until a fracture occurs. All of the posts go through this process simultaneously so that the stress build up is additive and can be a significant factor in the removal torque of the cap.
In some cases, thin continuous webs or lines of fracture have been proposed instead of posts for the frangible interconnecting portion between separable lower and upper cap portions. Even when the webs are very thin, however, they require relatively large forces to rupture them. As a result, serrations with a number of slits have been proposed to reduce the removal force which, in turn, can lead to premature rupturing and a false indication of tampering.
Another problem associated with molding plastic caps having thin interconnecting posts or lines of fracture is the greatly restricted flow of plastic through such portions to the thick portion below which constitutes the interference and tamper evidence means. This restricted flow can lead to undesirable external sink marks, internal voids or poor knitting of the plastic at weld lines, all of which can deteriously affect cap performance. To minimize such problems the interconnecting portions are sometimes made thicker than otherwise necessary or, from the standpoint of cap removal torques, desirable.
In making the present invention, moreover, it has been observed that in plastic caps having separable portions, the interconnecting portions frequently have excessive elongation. This can cause loss of thread engagement during twist-off cap removal before the cap lower portion is separated from its upper threaded portion, thereby frustrating cap removal. To offset this problem, this may require an increase in thread length resulting in a deeper skirt and higher cap costs in addition to the inconvenience of increased cap rotation during removal and reclosing.
Furthermore, plastic caps having separable portions with interconnecting serrated webs or posts are relatively expensive to manufacture, requiring complex injection molds to produce the desired slits or gaps which define the posts or web portions. Molds for these caps have significant sideways acting elements which are costly, which are subject to excessive wear from sliding friction, and which increase molding cycles and reduce the maximum number of cavities feasible for molding. Also, mating mold portions of the thin mold configurations needed to form the thin slits or gaps have a tendency to break down under production conditions with the potential of seriously altering the slit or gap dimensions and introducing inconsistencies to cap performance. As an alternative, the slits in the cap can be formed after molding using special knife edge slitting machines, but this introduces a separate operation with additional cost and quality control problems.
Thus, known tamper evident closures and packages and techniques for forming the closure are beset with drawbacks.